It really looks like it has herbicide damage. There appears to be a little damage to one of the others too. If someone is spraying weeds in the lawn or around the shrubs that is what would cause it. If no one is spraying anywhere near you then it could be a virus and you would need to remove the plants that should any damage.

I was using Preen Vegetable Garden Organic Weed Preventer in my hydrangea bed.  I quit using it when the leaves started curling which was about 3 years ago.  Would that have harmed it?  We have used curtail and roundup in the lawn but stay clear of the hydrangeas. If it has a virus is it urgent to remove the plant or can I leave it and see what happens to it next year?

Curtail is a farm labeled broadleaf weed killer. It would certainly cause herbicide damage to ornamentals. It is possible for it to drift easily. I would recommend that you stop using it in your yard. Even products that are labeled for lawns are able to do that damage. Here is the label. https://greenbook-assets.s3.amazonaws.com/uploads/D02-033-015_Curtail_Specimen_Label.pdf

I plan to remove the 2 hydrangea plants and their roots. Is it safe to plant new hydrangeas in the same location?  What precautions should I take?

You can plant new hydrangeas but if you spray an herbicide anywhere in the area you will risk damaging them again. If you are spraying you should consider covering them.